SCO Group, known until recently as Caldera International, has filed a lawsuit claiming over $1bn in damages from IBM.
The company claims that Big Blue misappropriated SCO's Unix technology to build up its Linux services business.
The lawsuit, which has been lodged with the State Court of Utah, claims "misappropriation of trade secrets, tortuous interference, unfair competition and breach of contract".
And SCO is not ruling out prosecutions of other Unix and Linux vendors.
Back in January, SCO chief executive Darl McBride said that the company had hired high-profile attorney David Boies to see whether various Unix versions, and even Windows, infringed on Unix intellectual property.
SCO alleges that IBM tried to improperly destroy the economic value of Unix, especially Unix on Intel, to benefit its new Linux services business.
As well as damages to be set at the trial of "not less than $1bn", SCO is demanding that IBM cease what it describes as anti-competitive practices.
The exact details were supplied in a letter to IBM, in which SCO insisted that, if the requirements are not met, it has the authority to revoke IBM's AIX licence in 100 days from the date of the letter.
In 1995 SCO purchased the rights to Unix and UnixWare, originally owned by AT&T Bell Laboratories, including source code, documentation, software development contracts, licences and other related intellectual property.
The company maintains that it is therefore the successor in interest to the Unix licences originally issued by AT&T Bell Laboratories to all its distributors, including Hewlett Packard, IBM, Silicon Graphics and Sun Microsystems.
SCO has over 30,000 contracts with Unix licensees. "Upholding these contracts is as important today as on the day they were signed," said McBride.
Other potential infringers are Apple with its Unix-based Mac OS X, Microsoft, and the Linux releases.
But SCO is also part of the UnitedLinux consortium and all Linux distributions share a common operating system kernel.
Boies is noted for working on the US Justice Department's antitrust case against Microsoft, and defending music-sharing site Napster. He also represented Al Gore in the Florida vote-counting controversy in the 2000 presidential elections.
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